Mobile communication systems, for example, Long Term Evolution (LTE) standardized by the 3GPP, widely use orthogonal multiple access in which multiple orthogonal signals not interfering with each other are used between a base station and user terminals (mobile stations). On the other hand, there has been proposed non-orthogonal multiple access using non-orthogonal signals to increase the capacity of a mobile communication system (for example, see Non-patent document 1).
The non-orthogonal multiple access is based on the premise of signal separation (interference canceller) through non-linear signal processing. For example, in the case of downlink, a base station simultaneously transmits non-orthogonal signals to multiple user terminals. Each of the user terminals performs signal processing to remove, from the received non-orthogonal signals, a signal addressed to a user terminal (at a cell edge) having a larger path loss than the user terminal itself, and then demodulates the resultant signal.